1. Technical Field
The present disclosure relates to an electrosurgical forceps and more particularly, the present disclosure relates to an apparatus and method for measuring the pressure between two jaw members when clamped on tissue or a tissue-like substance.
The present disclosure also relates to an apparatus and method for simulating pressure on tissue and tissue response.
2. Description of Related Art
Open and endoscopic electrosurgical forceps utilize both mechanical clamping action and electrical energy to effect hemostasis by heating the tissue and blood vessels to coagulate, cauterize and/or seal tissue. Open electrosurgical forceps, as the name infers, are typically utilized during open surgical procedure where a surgeon has open access to the surgical cavity. Endoscopic instruments, on the other hand, are typically inserted into the patient through a cannula, or port, which has been made with a trocar and the surgeon remotely actuates the instrument to treat tissue.
Due to the inherent spatial considerations of the surgical cavity, surgeons often have difficulty suturing vessels or performing other traditional methods of controlling bleeding, e.g., clamping and/or tying-off transected blood vessels. By utilizing an endoscopic electrosurgical forceps, a surgeon can either cauterize, coagulate/desiccate and/or simply reduce or slow bleeding simply by controlling the intensity, frequency and duration of the electrosurgical energy applied through the jaw members to the tissue. Most small blood vessels, i.e., in the range below two millimeters in diameter, can often be closed using standard electrosurgical instruments and techniques. However, if a larger vessel is ligated, it may be necessary for the surgeon to convert the endoscopic procedure into an open-surgical procedure and thereby abandon the benefits of endoscopic surgery. Alternatively, the surgeon can seal the larger vessel or tissue.
It is thought that the process of coagulating vessels is fundamentally different than electrosurgical vessel sealing. For the purposes herein, “coagulation” is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried. “Vessel sealing” or “tissue sealing” is defined as the process of liquefying the collagen in the tissue so that it reforms into a fused mass. Coagulation of small vessels is sufficient to permanently close them, while larger vessels need to be sealed to assure permanent closure.
In order to effectively seal larger vessels (or tissue) two predominant mechanical parameters are accurately controlled—the pressure applied to the vessel (tissue) and the gap distance between the electrodes—both of which are affected by the thickness of the sealed vessel. More particularly, accurate application of pressure is important to oppose the walls of the vessel; to reduce the tissue impedance to a low enough value that allows enough electrosurgical energy through the tissue; to overcome the forces of expansion during tissue heating; and to contribute to the end tissue thickness which is an indication of a good seal. It has been determined that a typical fused vessel wall is optimum between 0.001 and 0.006 inches. Below this range, the seal may shred or tear and above this range the lumens may not be properly or effectively sealed.
With respect to smaller vessels, the pressure applied to the tissue tends to become less relevant whereas the gap distance between the electrically conductive surfaces becomes more significant for effective sealing. In other words, the chances of the two electrically conductive surfaces touching during activation increases as vessels become smaller.
Accurate application of closure forces between electrically conductive surfaces, i.e., jaw members, is important to limit undesirable electrical abnormalities or tissue damage, e.g., it may cause the opposing electrodes to come into close contact with one another which may result in a short circuit and a small closure force may cause premature movement of the tissue during compression and prior to activation. As a result thereof, providing an instrument which consistently provides the appropriate closure force between opposing electrode within a preferred pressure range will enhance the chances of a successful seal.
It has been found that the pressure range for assuring a consistent and effective seal is between about 3 kg/cm2 to about 16 kg/cm2 and, desirably, within a working range of 7 kg/cm2 to 13 kg/cm2. Manufacturing an instrument which is capable of providing a closure pressure within this working range has been shown to be effective for sealing arteries, tissues and other vascular bundles.